This invention relates to a power wrench with torque control means, in particular a power wrench having a housing, a rotation motor, an output shaft, and a power transmission for coupling the motor to the output shaft and which includes a torque limiting mechanism comprising a cam means and a cam means biassing compression spring which is pretensioned between a thrust member associated with the cam means and an adjustable support member.
In tools of the above type, the degree of pretension of the cam biassing spring, i.e. the length of the spring, corresponds directly to the torque level at which the torque limiting mechanism is activated to accomplish termination of the torque delivery to the output shaft. Changes in the spring pretension is accomplished by adjustment of the support member, and for obtaining an easy checking of the actual setting of the spring pretension and, thereby, the output torque of the tool, there are provided marks on the support member and on the housing. The mark on the support element is visible from outside the tool through an aperture in the housing.
However, due to the outcome of tolerances on the details comprised in the tool, a certain setting of the support element relative to the tool housing of one tool represents a spring pretension level that is different from that of another tool with the same setting of the support element. Accordingly, the output torque level varies from one tool to another despite a uniform setting of the support element. This means that there is a problem and a difficulty in obtaining a reliable basic setting of the output torque of a tool.
The main object of the invention is to solve the above problem by providing a power wrench with a new and improved mark means which is independent of deviations caused by the outcome of tolerances on the details comprised in the tool, and which enables a correct and reliable basic setting of the torque limiting mechanism, which corresponds to a desired nominal output torque level of the tool.
Further objects and advantages of the invention will appear from the following detailed description of a prefered embodiment of the invention.